The present invention relates to a safety device for the steering units of bicycles, motorcycles and the like provided with a steering tube within which a sleeve is rotatably mounted with the interposition of rolling bearings, an upper bearing comprising a first ring mounted on the steering tube, and a second ring screwed onto a threaded portion of the sleeve and locked in position by a lock nut.
In current bicycles, particularly bicycles of the "mountain bike" type used mainly on rough tracks, the lock nut and consequently the ring of the upper bearing which is screwed onto the sleeve of the fork often work loose as a result of the vibrations to which the steering unit is subjected. If this loosening is not corrected promptly by the adjustment of the play in the steering bearings, it may cause damage to the rolling tracks and give rise to the malfunctioning of the steering unit.